Liquid crystal displays (LCDs) are so-called non-self-emitting displays, which in general need a backlight module for the supply of light in order to display images. A typical backlight module generally includes a cold cathode fluorescent lamp (CCFL), and a balance controlling circuit for controlling operation of the CCFL. The precision of the current provided by the balance controlling circuit needs to meet a threshold requirement whereby the CCFL provides uniform, high luminance light, and whereby the lifespan of the CCFL can also be prolonged.
Referring to FIG. 3, a conventional balance controlling circuit 10 includes a transformer T1, six resistors R1, R2, R3, R4, R5, and R6, four capacitors C1, C2, C3, and C4, and a first inductor TC1 and a second inductor TC2.
The transformer T1 includes a first input 11, a second input 12, a first output 13, and a second output 14. The first inductor TC1 includes a first port 21, a second port 22, a third port 23, and a fourth port 24. The second inductor TC2 includes a first port 31, a second port 32, a third port 33, and a fourth port 34.
The first and second inputs 11, 12 of the transformer T1 connect to an external circuit, for example, a power supply (not shown). The first output 13 of the transformer T1 is grounded, and the second output 14 of the transformer T1 connects to one port of the capacitors C1 and C2 respectively. Another port of the capacitor C1 is connected in parallel to the capacitors C3, C4, which are both grounded. Said one port of the capacitor C2 also connects to the second port 22 of the first inductor TC1, and another port of the capacitor C2 connects to the fourth port 24 of the first inductor TC1 and the second port 32 of the second inductor TC2 respectively. The resistors R1, R2 are connected in series between the fourth and third ports 24, 23 of the first inductor TC1. The third port 23 of the first inductor TC1 connects to a first CCFL (not shown) via a first output port I11.
The first port 21 of the first inductor TC1 connects to the fourth port 34 of the second inductor TC2. The resistors R3, R4 are connected in series between the second port 22 of the first inductor TC1 and the third port 33 of the second inductor TC2. The third port 33 of the second inductor TC2 also connects to a second CCFL (not shown) via a second output port I12.
The resistors R5, R6 are connected in series between the first and second ports 31, 32 of the second inductor TC2. The first port 31 of the second inductor TC2 also connects to a third CCFL (not shown) via a third output port I13.
The precision of the current for the CCFLs provided by the balance controlling circuit 10 can generally only be regulated to ±0.6 mA. This level of precision may not be considered satisfactory for certain backlight modules having high current precision requirements.
Accordingly, what is needed is a balance controlling circuit configured to be able to provide high precision operational capability.